1. Technical Field
The present invention relates to a search frequency correction method, a positioning method, a program, and a receiving apparatus.
2. Related Art
As a type of a receiving apparatus adapted to receive a signal modulated by a direct sequence spread spectrum method, there exists a positioning apparatus receiving a positioning signal spread-modulated with a pseudo random noise (PRN) code to perform positioning. For example, Global Positioning System (GPS) positioning apparatuses receiving GPS satellite signals transmitted from GPS satellites to perform positioning are well known to the public.
In order for capturing the positioning signal out of the received signals, it is required to execute correlation calculation between the received signals and the replica code of the spread code at a predetermined search frequency while shifting the phase of the replica code, and extract the phase (a so-called code phase) with which the correlation value becomes the maximum. However, since the capturing of the positioning signal results in failure unless the search frequency is set appropriately, various technologies for determining the search frequency have been invented (e.g., JP-A-8-146113 (Document 1)).
In the technology disclosed in the Document 1, the search frequencies different from each other are set in respective satellites taking the Doppler frequency caused by the variation in the relative position between the positioning satellite and the positioning apparatus and the oscillation frequency of the clock incorporated in the positioning apparatus into consideration, thereby attempting to capture the satellite. Further, according to the technology, when capturing of one satellite is successful, the search frequencies of other satellites are variably set based on the offset of the oscillation frequency of the clock having been set for the capturing. In the technology, in order for adjusting the search frequencies, it is required to capture at least either one of the satellites. Further, since the variation in the relative position to the positioning apparatus is different between the positioning satellites, there is also caused a problem that the search frequency for one satellite thus captured is not necessarily suitable for the search frequencies for other satellites.